Infection with adenovirus, a common childhood virus, is the leading hypothesis for recent cases of severe hepatitis of unknown origin in children that have led to at least six deaths, U.S. health officials said on May 20.

The European Center for Disease Prevention and Control said the number of unusual pediatric hepatitis cases reached 450, double the number reported two weeks earlier.

AstraZeneca’s Covid-19 vaccine accurately follows the genetic instructions programmed into AZD1222 by the developers to successfully provoke a strong immune response, according to a detailed analysis carried out by independent UK scientists.